The present invention relates to a filter having a filter housing having an inlet for liquid to be filtered and having an outlet for filtered liquid, having an exchangeable filter insert that separates an unfiltered side and a filtered side of the filter from one another, and having a filter bypass valve that is made up of a valve seat and a valve body that is guided so as to be movable relative to the valve seat and is preloaded in the closing direction. Moreover, the present invention relates to a filter insert that works together with the above-named filter.
A first filter of the type named above is known from U.S. Pat. No. 6,579,448 B2. This document discloses a filter having an exchangeable filter insert and having a filter bypass valve. A valve seat of the filter bypass valve is situated on the filter insert, specifically on its upper end plate. A valve body, a spring that preloads the valve body in the closing direction, and a spring support are fashioned so as to be fixed to the housing. Specifically, the spring support is provided on a central pipe socket or supporting element fixed to the housing.
Another filter is known from U.S. Pat. No. 6,685,829 B1. This document discloses a filter having an exchangeable filter insert and having a filter bypass valve. A valve seat is provided on the filter insert, here specifically on its lower end plate. A valve body, a spring that preloads the valve body in the closing direction, and a spring support are here realized so as to be fixed to the housing. The valve body is fashioned on a central pipe socket that is fixed to the housing but is capable of displacement in an axially limited manner. The spring is situated as a pressure spring between the pipe socket and the housing.
DE 10 2009 021 973 A1 discloses a further filter having an exchangeable filter insert and having a filter bypass valve. The valve seat, the valve body, the spring, and a first spring support of the filter bypass valve are here parts of the filter insert. On a central pipe socket fixed to the filter, a second spring support is provided that, when the filter insert is placed onto the pipe socket during installation of the filter insert in the filter housing, takes over the supporting of the spring and increases its prestressing.
From U.S. Pat. No. 8,123,937 B2, additional filters are known having an exchangeable filter insert and having a filter bypass valve. The valve seat and the valve body of the filter bypass valve are here each provided on the filter insert, specifically on its upper end plate. A pressure spring that preloads the valve body in the closing direction, and an additional actuating element that, when the filter insert is in place, transmits the spring force to the valve body, are configured so as to be fixed to the housing, specifically in a central supporting element fixed to the housing.
WO2006/112 853 A1 also discloses a filter having an exchangeable filter insert and having a filter bypass valve. Here, the valve seat is provided on the filter insert, specifically on its upper end plate. A valve body, a spring that preloads the valve body in the closing direction, and a spring support are realized so as to be fixed to the housing. Specifically, the valve body and the spring are guided in an upper end region of a central supporting element that is fixed to the housing. The spring support is also fashioned on the supporting element.
In filters of the type described above, in which the valve seat on the exchangeable filter insert and the valve body are realized so as to be fixed to the filter, after each change of filter insert there is a valve mating with interacting valve components that is not checked beforehand for tightness and is also not capable of being checked ahead of time for tightness. In practice, this results relatively frequently in filter bypass valves that are not tight in their closing position, through which, undesirably, there is a constant flow of liquid that is unfiltered and that impairs the purity necessary for the actually intended use of the filtered liquid. The solutions known from the existing art as indicated in the three last-named documents above, in which in addition to the valve seat the valve body is also provided on the exchangeable filter insert, require an additional actuating element, and in part even an additional spring, which disadvantageously increases the number of components and thus the production and assembly costs. Also, in this way the filter inserts require significantly more outlay for their construction, and are therefore more expensive, which has noticeable effects every time the filter insert is exchanged. Finally, the known filters have the disadvantage that the opening pressure of the filter bypass valve can be modified only with a relatively high outlay.